package bite;
import java.util.*;
/**
 * Creared with IntelliJ IDEA.
 * Description:【养兔子】一只成熟的兔子每天能产下一胎兔子。每只小兔子的成熟期是一天。 某人领养了一只小兔子，请问第N天以后，他将会得到多少只兔子。
 * User:yxd
 * Date:2022-06-10
 * Time:16:49
 */
public class Day34_2 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        while(input.hasNextInt()){
            int n = input.nextInt();
            //F(i)表示当前有多少只兔子
            //F(i) = F(i - 1) + F(i - 2)
            //F(1) = 1 F(2) = 2 F(3) = 3
            long[] dp = new long[91];
            dp[0] = 0l;
            dp[1] = 1l;
            dp[2] = 2l;
            for(int i = 3;i <= 90;i ++){
                dp[i] = dp[i - 1] + dp[i - 2];
            }
            System.out.println(dp[n]);
        }
    }
}
